Disc reproduction device

ABSTRACT

The present invention provides a disk playback device comprising a control circuit  7  for determining an optimum value of offset for a focus error signal based on amplitude values of a tracking error signal or an RF signal fed from an optical head  5 , and making an offset adjustment with reference to the optimum value. The control circuit  7 , in signal reproduction, approximates the relationship between offset values and the amplitude values to a quadratic curve with reference to three different offset values and three amplitudes at the respective offset values, repeats a calculation of an optimum offset value corresponding to the peak of the quadratic curve, and sets the three different first to third offset values respectively at an optimum value obtained in a previous optimum offset value calculation processing, and second and third offset values set in the previous optimum offset value calculation processing.

TECHNICAL FIELD

The present invention relates to disk playback devices for reproducingsignals from a disk by irradiating the disk with a laser beam from anoptical head.

BACKGROUND ART

For use as recording media in disk recording-playback devices,magneto-optical disks have been developed which permit rewriting andhave a great memory capacity and high reliability. Such disks have foundwide use as external memories in computers and audio visual devices.

Developed especially in recent years are techniques for achievingimproved recording densities by forming lands 11 and grooves 12alternately on a signal bearing surface of a magneto-optical disk 1 asshown in FIG. 12 and recording signals on both the lands 11 and thegrooves 12. The lands 11 and the grooves 12 are wobbled as illustrated,and the wobbling frequency is a predetermined center frequency asfrequency-modulated. A wobble signal is detected by signal reproduction,and the rotation of the magneto-optical disk is so adjusted that thewobble signal has the center frequency at all times, whereby constantlinear velocity control is realized. Various items of information(wobble information) such as address information are contained in thewobble signal which is frequency-modulated as stated above. Variouscontrol operations are realized based on the wobble information at thetime of signal reproduction.

When disk recording-playback devices are in operation for reproducing orrecording signals, focus servo or tracking servo is performed for theactuator incorporated in the optical head, based on focus error (FE)signals and tracking error (TE) signals. When the diskrecording-playback device is initiated into operation, an offsetadjustment is made for focusing or tracking based on the TE signals andRF signals to thereby effect accurate focus servo and tracking servo.

In a process for determining an optimum offset value for a focus errorbased on the TE signal, as seen in FIG. 19, first, focus offset valuesare respectively set at at least five different values P₀ to P₄ centeredabout an initial value P₀, and amplitude values of the TE signal at therespective offset values are measured. Among said at least five pointsmeasured, a first point is set at a point having the maximum amplitudevalue, a second point is set at a point having an offset value smallerthan the offset value P₀ at the first point and an amplitude value notgreater than a value (T₀−5) obtained by subtracting a predeterminedvalue from an amplitude value T₀ at the first point, a third point isset at a point having an offset value greater than the offset value P₀at the first point and an amplitude value not greater than the value(T₀−5) obtained by subtracting the predetermined value from theamplitude value T₀ at the first point. With reference to the offsetvalues P₀, P₁, P₄ and the amplitude values T₀, T₁, T₄ at the respectivethree points, a quadratic curve representing the relationship betweenthe offset values and the amplitude values is determined. An offsetvalue corresponding to the peak of the quadratic curve is determined asan optimum offset value P_(opt1). A procedure for determining an optimumoffset value based on the RF signals is the same as the above.

FIGS. 13 to 15 show a focus offset adjustment procedure to be executedbased on the TE signals when the disk recording-playback device is intoan initiation operation. First in steps S91 to S94 in FIG. 13, focusoffset values are respectively set at an initial value P₀, a value P₁smaller than the initial value by eight steps, a value P₂ smaller thanthe initial value by four steps, a value P₃ greater than the initialvalue by four steps, and a value P₄ greater than the initial value byeight steps, and amplitude values T₀ to T₄ are measured at therespective offset values. Among these five points measured, thereafter,a first point is set at a point having the maximum amplitude value. Afirst offset value P_(max) is set at an offset value at the first point.A first amplitude value T_(max) is set at an amplitude value at thefirst point.

Subsequently in step S95, an inquiry is made as to whether a secondpoint having an offset value P_(x) smaller than the first offset valueP_(max) and an amplitude value T_(x) smaller than the first amplitudevalue T_(max) by five steps or more is included in four measured pointsother than the first point. If the inquiry is answered in theaffirmative, step S96 follows to set a second offset value P_(A) at theoffset value P_(x) at the second point, set a second amplitude valueT_(A) at the amplitude value T_(x) at the second point, and set to“TRUE” a P_(A) _(—) flag indicating whether the second offset valueP_(A) is obtained, thereafter followed by step S97.

In step S97, an inquiry is made as to whether a third point having anoffset value PX greater than the first offset value P_(max) and anamplitude value T_(x) smaller than the first amplitude value T_(max) byfive steps or more is included in the four measured points other thanthe first point. If the inquiry is answered in the affirmative, step S98follows to set a third offset value P_(B) at the offset value P_(x) atthe third point, set a third amplitude value T_(B) at the amplitudevalue T_(x) at the third point, and set to “TRUE” a P_(B) _(—) flagindicating whether the third offset value P_(B) is obtained, thereafterfollowed by step S99 shown in FIG. 14.

When the second point and the third point are both included in the fourmeasured points other than the first point, answers to inquiries in stepS99 in FIG. 14 and in step S106 in FIG. 15 are affirmative, followed bystep S113. With reference to data on the first to third points (P_(max),T_(max)), (P_(A), T_(A)) and (P_(B), T_(B)) which are included in thefive measured points, the relationship between the offset values and theamplitude values is approximated to a quadratic curve, and an offsetvalue corresponding to the peak of the quadratic curve is calculated asan optimum offset value P_(opt), to terminate the procedure.

On the other hand, when the second point is not included in the fourmeasured points other than the first point, an answer to the inquiry instep S99 in FIG. 14 is negative. In steps S100 to S105, an offset valueP is decreased every four step starting from a value smaller than theinitial value P₀ by 12 steps, to thereby vary the offset value untilwhen the amplitude value T becomes a value smaller than the firstamplitude value T_(max) by five steps or more. Then the offset value andamplitude value concerned are respectively set at a second offset valueP_(A) and a second amplitude value T_(A). Accordingly the second pointis retrieved. When, in step S113 in FIG. 15, the relationship betweenthe offset values and the amplitude values is approximated to aquadratic curve, the data (P_(A), T_(A)) at the retrieved second pointis used. Incidentally, in retrieving the second point, in the case wherethe offset value P is smaller than the initial value P₀ by 20 steps ormore to make the answer to step S101 affirmative, or in the case wherethe amplitude value T is not greater than a lower limit value T_(L) tomake the answer to step S103 affirmative, focus servo deviates toterminate the procedure.

Furthermore, when the third point is not included in the four measuredpoints other than the first point, an answer to the inquiry in step S106in FIG. 15 is negative. In steps S107 to S112, an offset value P isincreased every four step starting from a value greater than the initialvalue P₀ by 12 steps, to thereby vary the offset value until when theamplitude value T becomes a value smaller than the first amplitude valueT_(max) by five steps or more. Then the offset value and amplitude valueconcerned are respectively set at a third offset value P_(B) and a thirdamplitude value T_(B). Accordingly the third point is retrieved. When,in step S113, the relationship between the offset values and theamplitude values is approximated to a quadratic curve, the data (P_(B),T_(B)) at the retrieved third point is used. Incidentally, in retrievingthe third point, in the case where the offset value P is greater thanthe initial value P₀ by 20 steps or more to make the answer to step S108affirmative, or in the case where the amplitude value T is not greaterthan a lower limit value T_(L) to make the answer to step S110affirmative, focus servo deviates to terminate the procedure.

According to the above procedure, the optimum offset value P_(opt) forthe focus error is determined based on the TE signals, and an offsetadjustment for focusing is made based on the optimum offset valueP_(opt). According to the same procedure, an optimum offset value forthe focus error is determined based on the RF signals, and an offsetadjustment for focusing is made based on the optimum offset value. Thedisk recording-playback device starts signal reproduction or signalrecording after the offset adjustment for focusing thus made.

In a usual operation for signal reproduction or signal recording,variations in the ambient temperature, however, lead to the distortionof the housing or parts of the optical head, a shift of position of theoptical sensor, variations in the laser wavelength, etc., altering theoffset value from an optimum value and consequently impairing theaccuracy of focus servo. If the offset value deviates from the optimumvalue greatly, the bit error rate of reproduced signal exceeds aprescribed value, presenting difficulty in effecting normal reproductionand recording.

In the usual operation, an offset adjustment for focusing is made everytime a temperature of the disk varies by a predetermined temperature ormore.

In a process of determining an optimum offset value for a focus errorbased on the TE signals for the usual operation, as seen in FIG. 20,first, focus offset values are respectively set at at least fivedifferent values P_(opt1), P₁′ to P₄′, centered about the optimum offsetvalue P_(opt1), i.e., the set value concerned, determined in a previousoffset adjustment processing, and amplitude values of the TE signals atthe respective offset values are measured. Among said at least fivepoints measured, a first point is set at a point having the maximumamplitude value, a second point is set at a point having an offset valuesmaller than the offset value P_(opt1) at the first point and anamplitude value not greater than a value (T_(opt1)−5) obtained bysubtracting a predetermined value from an amplitude value T_(opt1) atthe first point, a third point is set at a point having an offset valuegreater than the offset value P_(opt1) at the first point and anamplitude value not greater than the value (T_(opt1)−5) obtained bysubtracting the predetermined value from the amplitude value T_(opt1) atthe first point. With reference to the offset values P_(opt1), P₁′, P₄′and the amplitude values T_(opt1), T₁′, T₄′ at the respective threepoints, a quadratic curve representing the relationship between theoffset values and the amplitude values is determined. An offset valuecorresponding to the peak of the quadratic curve is determined as anoptimum offset value P_(opt2). A procedure of determining an optimumoffset value based on the RF signals is the same as the above.

FIGS. 16 to 18 show a focus offset adjustment procedure to be executedbased on the TE signals when temperature variations in excess of orequal to a predetermined value (=5° C.) occur in a usual operation afterthe system's initiation into operation. First in steps S121 to S124,focus offset values are respectively set at a set value concerned P₀′, avalue P₁′ smaller than the set value by eight steps, a value P₂′ smallerthan the set value by four steps, a value P₃′ greater than the set valueby four steps, and a value P₄′ greater than the set value by eightsteps, and amplitude values T₀′ to T₄′ are measured at the respectiveoffset values. Among these five points measured, thereafter, the maximumamplitude value is a first point. An offset value at the first point isa first offset value P_(max)′. An amplitude value at the first point isa first amplitude value T_(max)′.

Subsequently in step S125, an inquiry is made as to whether a secondpoint having an offset value P_(x)′ smaller than the first offset valueP_(max)′ and an amplitude value T_(x)′ smaller than the first amplitudevalue T_(max)′ by five steps or more is included in four measured pointsother than the first point. If the inquiry is answered in theaffirmative, step S126 follows to set a second offset value P_(A) at theoffset value P_(x)′ at the second point, set a second amplitude valueT_(A) at the amplitude value T_(x)′ at the second point, and set to“TRUE” a P_(A) _(—) flag indicating whether the second offset valueP_(A) is obtained, thereafter followed by step S127.

In step S127, an inquiry is made as to whether a third point having anoffset value P_(x)′ greater than the first offset value P_(max)′ and anamplitude value T_(x)′ smaller than the first amplitude value T_(max)′by five steps or more is included in the four measured points other thanthe first point. If the inquiry is answered in the affirmative, stepS128 follows to set a third offset value P_(B) at the offset valueP_(x)′ at the third point, set a third amplitude value T_(B) at theamplitude value T_(x)′ at the third point, and set to “TRUE” a P_(B)_(—) flag indicating whether the third offset value P_(B) is obtained,thereafter followed by step S129 shown in FIG. 17.

When the second point and the third point are included in the fourmeasured points other than the first point, answers to inquiries in stepS129 in FIG. 17 and in step S136 in FIG. 18 are affirmative, followed bystep S143. With reference to data on the first to third points(P_(max)′, T_(max)′), (P_(A), T_(A)) and (P_(B), T_(B)) which areincluded in the five measured points, the relationship between theoffset values and the amplitude values is approximated to a quadraticcurve, and an offset value corresponding to the peak of the quadraticcurve is calculated as an optimum offset value P_(opt)′, to terminatethe procedure.

On the other hand, when the second point is not included in the fourmeasured points other than the first point, a second point is retrievedaccording to the same procedure as that in an initiation operation asshown in steps S130 to S135 in FIG. 17. When, in step S143 in FIG. 18,the relationship between the offset values and the amplitude values isapproximated to a quadratic curve, data (P_(A), T_(A)) at the retrievedsecond point is used.

Furthermore, when the third point is not included in the four measuredpoints other than the first point, a third point is retrieved accordingto the same procedure as that in an initiation operation as shown insteps S137 to S142 in FIG. 18. When, in step S143, the relationshipbetween the offset values and the amplitude values is approximated to aquadratic curve, data (P_(B), T_(B)) at the retrieved third point isused.

According to the above procedure, the optimum offset value P_(opt)′ fora focus error is determined based on the TE signals, and the focusoffset adjustment is made based on the optimum offset value P_(opt)′.According to the same procedure, an optimum offset value for a focuserror is determined based on the RF signals, and the focus offsetadjustment is made based on the optimum offset value. The diskrecording-playback device starts signal reproduction or signal recordingafter the offset adjustment for focusing thus made. When the diskrecording-playback device is in the usual operation, the focus offsetadjustment is thus made, consequently effecting focus servo with highaccuracy at all times despite variations in temperature of themagneto-optical disk.

However, the disk recording-playback device described has the followingproblem: in the offset adjustment procedure of the usual operation, therelationship between the offset values and the amplitude values isapproximated to a quadratic curve with reference to the previous optimumoffset value P_(opt1), and the second and third offset values P₁′, P₄′each having an amplitude value smaller than the amplitude value T_(opt1)at the offset value P_(opt1) by a predetermined value or more, as shownin FIG. 20, to increase accuracy of the quadratic curve. For obtainingthe second and third offset values P₁′, P₄′, amplitude values at atleast five different offset values P_(opt1) and P₁′ to P₄′ need bemeasured, requiring a long period of time for determining the quadraticcurve, thereby entailing the problem of a long period of time taken forthe calculation of the optimum offset value.

An object of the present invention is to provide a disk playback devicewhich is adapted to determine the optimum offset value for the errorsignal in a short period of time when in the usual operation.

DISCLOSURE OF THE INVENTION

The present invention provides a disk playback device comprising acalculation processing circuit for determining an optimum value ofoffset for an error signal based on an amplitude value of the errorsignal in accordance with focus deviation or tracking deviation of anoptical head, or an amplitude value of an output signal of the opticalhead, and making an offset adjustment based on the optimum offset value.The calculation processing circuit approximates to a quadratic curve therelationship between offset values and the amplitude values in signalreproduction, and repeats calculation of the optimum offset values basedon the quadratic curve. The calculation processing circuit comprises:

calculation processing means for approximating to a quadratic curve therelationship between the offset values and the amplitude values withreference to three different offset values and three amplitude values atthe respective offset values, and calculating an offset valuecorresponding to the peak of the quadratic curve as the optimum offsetvalue, and

value setting means for setting the three different offset values: afirst offset value; a second offset value smaller than the first offsetvalue and having an amplitude value smaller than an amplitude value atthe first offset value by a predetermined value or more; a third offsetvalue greater than the first offset value and having an amplitude valuesmaller than an amplitude value at the first offset value by apredetermined value or more, and setting the three amplitude valuesrespectively at three amplitude values at the first to third offsetvalues. The value setting means sets the first offset value at anoptimum offset value obtained in a previous optimum offset valuecalculation processing, and sets the second and third offset valuesrespectively at second and third offset values set in a previous optimumoffset value calculation processing.

According to an optimum offset value calculation processing in a usualreproduction operation of the present invention, the first offset valueis set at an optimum offset value obtained in a previous optimum offsetvalue calculation processing, and the second and third offset values arerespectively set at second and third offset values set in a previousoptimum offset value calculation processing.

Incidentally, the second and third offset values set in the previousoptimum offset value calculation processing each has an amplitude valuesmaller than an amplitude value at the first offset value by apredetermined value or more. Further, the offset value corresponding tothe peak of the quadratic curve is calculated as the optimum offsetvalue, so that the optimum offset value obtained in the previous optimumoffset value calculation processing has an amplitude value greater thanthe amplitude value at the first offset value. Accordingly, the secondand the third offset values each has an amplitude value smaller than theamplitude value at the optimum offset value by a predetermined value ormore.

Furthermore, when the disk playback device is in a usual reproductionoperation, the quadratic curve representing the relationship between theoffset values and the amplitude values shows little change. Therefore,also in the current offset value calculation processing, the amplitudevalues at the previous second and third offset values have a very highpossibility of being smaller than the amplitude value at the previousoptimum offset value by a predetermined value or more, whereby thequadratic curve can be determined with high accuracy with reference tothe previous optimum offset value, the second and third offset values,and the amplitude values at the respective offset values.

According to the optimum offset value calculation processing of thepresent invention, if the amplitude values at at least three offsetvalues, i.e., the previous optimum offset value, the previous second andthird offset values, are measured, the quadratic curve can be determinedwith high accuracy with reference to these three offset values and threeamplitude values. Thus a period of time required for the determinationof the quadratic curve is made shorter than conventionally, because,with the conventional device, the measurement of amplitude values at atleast five different offset values is required. This makes shorter aperiod of time taken for the calculation of the optimum offset value.

Stated specifically, the calculation processing circuit comprises:

first checking means for checking whether an amplitude value at theprevious second offset value is smaller than an amplitude value at theprevious optimum offset value by a predetermined value or more,

second checking means for checking whether an amplitude value at theprevious third offset value is smaller than an amplitude value at theprevious optimum offset value by a predetermined value or more, thevalue setting means comprising:

second offset value setting means for retrieving an offset value havingan amplitude value smaller than the amplitude value at the previousoptimum offset value by a predetermined value or more when the amplitudevalue at the previous second offset value is not found to be smallerthan the amplitude value at the previous optimum offset value by apredetermined value or more, and setting a second offset value at theretrieved offset value, and

third offset value setting means for retrieving an offset value havingan amplitude value smaller than the amplitude value at the previousoptimum offset value by a predetermined value or more when the amplitudevalue at the previous third offset value is not found to be smaller thanthe amplitude value at the previous optimum offset value by apredetermined value or more, and setting a third offset value at theretrieved offset value.

As described above, also in the current offset value calculationprocessing, the amplitude values at the previous second and third offsetvalues have a very high possibility of being smaller than the amplitudevalue at the previous optimum offset value by a predetermined value ormore, but the amplitude values fail to be smaller than the value by apredetermined value or more as the case may be. In such a case, when thequadratic curve is determined with reference to the previous optimumoffset value and the previous second and third offset values, thequadratic curve has a low accuracy, thereby impairing the accuracy ofthe optimum offset value corresponding to the peak of the quadraticcurve.

According to the specific construction described, when the amplitudevalue at the previous second offset value is not found to be smallerthan the amplitude value at the previous optimum offset value by apredetermined value or more, retrieved is an offset value having anamplitude value smaller than the amplitude value at the previous optimumoffset value by a predetermined value or more, to determine a quadraticcurve by setting a second offset value at the retrieved offset value.Furthermore, when the amplitude value at the previous third offset valueis not found to be smaller than the amplitude value at the previousoptimum offset value by a predetermined value or more, retrieved is anoffset value having an amplitude value smaller than the amplitude valueat the previous optimum offset value by a predetermined value or more,to determine a quadratic curve by setting a third offset value at theretrieved offset value. Accordingly, the quadratic curve can bedetermined with high accuracy, to thereby obtain the optimum offsetvalue with high accuracy at all times.

Stated further specifically, the disk playback device comprisestemperature detection means for detecting a temperature of the disk. Thecalculation processing circuit calculates the optimum offset value everytime the disk is varied in temperature by a predetermined temperaturevalue.

According to the specific construction described, every time the disk isvaried in temperature by a predetermined temperature value, the optimumoffset value is obtained. Based on the optimum offset value obtained, anoffset adjustment is made. This reproduces an error signal given theoptimum offset adjustment in accordance with temperature variations,whereby focusing of the optical head or tracking is controlled with highaccuracy based on the error signal.

As described above, with the disk playback device of the presentinvention, the optimum value of offset for the error signals can beobtained in a short period of time when the device is in the usualoperation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a construction of a diskrecording-playback device according to the present invention;

FIG. 2 is a flow chart showing a procedure to be executed when the diskrecording-playback device is initiated into operation;

FIG. 3 is a flow chart showing a first part of a specific procedure offocus offset adjustment processing to be executed when the device isinitiated into operation;

FIG. 4 is a flow chart showing a second part of the procedure;

FIG. 5 is a flow chart showing a third part of the procedure;

FIG. 6 is a flow chart showing a procedure to be executed when the diskrecording-playback device is in a usual operation;

FIG. 7 is a flow chart showing a first part of a specific procedure offocus offset adjustment processing to be executed when the device is inthe usual operation;

FIG. 8 is a flow chart showing a second part of the procedure;

FIG. 9 is a flow chart showing a third part of the procedure;

FIG. 10 is a graph illustrating the procedure of focus offset adjustmentprocessing to be executed when the device is initiated into operation;

FIG. 11 is a graph illustrating a procedure of offset adjustmentprocessing to be executed when the device is in the usual operation;

FIG. 12 is an enlarged perspective view showing lands and grooves formedon a magneto-optical disk;

FIG. 13 is a flow chart showing a first part of a specific procedure offocus offset adjustment processing to be executed when a conventionaldisk recording-playback device is initiated into operation;

FIG. 14 is a flow chart showing a second part of the procedure;

FIG. 15 is a flow chart showing a third part of the procedure;

FIG. 16 is a flow chart showing a first part of a specific procedure offocus offset adjustment processing to be executed when the diskrecording-playback device is in a usual operation;

FIG. 17 is a flow chart showing a second part of the procedure;

FIG. 18 is a flow chart showing a third part of the procedure;

FIG. 19 is a graph illustrating a procedure of focus offset adjustmentprocessing to be executed when the device is initiated into operation;

FIG. 20 is a graph illustrating a procedure of focus offset adjustmentprocessing to be executed when the device is in the usual operation.

BEST MODE OF CARRYING OUT THE INVENTION

With reference to the drawings, a detailed description will be givenbelow of the present invention as embodied into disk recording-playbackdevices for use with magneto-optical disks serving as recording media.

FIG. 1 shows a disk recording-playback device embodying the inventionand comprising a spindle motor 2 for rotatingly driving amagneto-optical disk 1, a magnetic head 3 and an optical head 5 providedabove and below the magneto-optical disk 1, respectively. A magnetichead drive circuit 4 is connected to the magnetic head 3 while a laserdrive circuit 6 is connected to the optical head 5. Connected to themagnetic head drive circuit 4 and the laser drive circuit 6 is a controlcircuit 7, which controls recording/reproduction operations of signals.An output signal of the optical head 5 is fed to the control circuit 7,and output to a subsequent circuit as reproduced data after processingsuch as amplification, detection of reproduction signals, and errorcorrection.

Further, a servo circuit 9 is connected to the spindle motor 2 and theoptical head 5. An FE signal and a TE signal obtained from the outputsignal of the optical head 5 are fed to the servo circuit 9 from thecontrol circuit 7. In response to the FE signal and TE signal, focusservo and tracking servo for an actuator (not shown) provided for theoptical head 5 are executed. Furthermore, an external synchronizingsignal is fed to the servo circuit 9 from the control circuit 7, and therotation of the spindle motor 2 is controlled based on the signal.

Furthermore, provided opposed to the magneto-optical disk 1 is atemperature sensor 8 for measuring a temperature of the magneto-opticaldisk 1. An output terminal of the temperature sensor 8 is connected tothe control circuit 7, where, based on temperature data obtained fromthe temperature sensor 8, an offset adjustment procedure as will bedescribed below is executed, determining optimum offset valuesrespectively for the FE signal and the TE signal, making the offsetadjustment for the FE signal and the TE signal with reference to therespective optimum offset values. The FE signal and the TE signal giventhe offset adjustment are input to the servo circuit 9, and are fed tofocus servo and tracking servo.

FIG. 2 shows a procedure to be executed by the control circuit 7 in aninitiation into operation of the disk recording-playback device. Whenthe device is turned on, first in step S1 various gains of the servocircuit 9 are set at initial values. In step S2 an offset value forfocus is adjusted based on the TE signal.

Next in step S3 an offset value for tracking is adjusted based on the TEsignal, and thereafter in step S4 each of a recording power andreproduction power is set at an initial value. Then in step S5 a gainnecessary for reading out address information recorded on themagneto-optical disk (address gain) and a gain necessary for reading outan FCM (fine clock mark) (FCM gain) are set at initial values.

Subsequently in step S6 the offset value for focus is adjusted based onthe RF signal, and thereafter in step S7 the reproduction power isadjusted. Then in step S8 a servo gain for focus and a servo gain fortracking are adjusted, and thereafter in step S9 the address gain andFCM gain are adjusted. A series of the adjustment processing of step S6to step S9 is executed for each of the lands and grooves of the testtracks pre-provided on the magneto-optical disk.

Then in step S10 the recording power is adjusted for each of the landsand grooves of the test tracks. In step S11 current values of parametersadjusted as described are checked. Lastly in step S12 the current valuesof those parameters are stored in a built-in memory, and thereafter instep S13 a current disk temperature T₀ is stored in the built-in memoryto terminate the procedure.

In the focus offset adjustment processing of step S2 and step S6described, as seen in FIG. 10, focus offset values are respectively setat at least five different values P₀ to P₄ centered about an initialvalue P₀, and amplitude values of the TE signal or the RF signal at therespective offset values are measured. Among said at least five pointsmeasured, a first point is set at a point having the maximum amplitudevalue, a second point is set at a point having an offset value smallerthan the offset value P₀ at the first point and an amplitude value notgreater than a value (T₀−5) obtained by subtracting a predeterminedvalue from an amplitude value T₀ at the first point, a third point isset at a point having an offset value greater than the offset value P₀at the first point and an amplitude value not greater than the value(T₀−5) obtained by subtracting the predetermined value from theamplitude value T₀ at the first point. With reference to the offsetvalues P₀, P₁, P₄ and the amplitude values T₀, T₁, T₄ at the respectivethree points, a quadratic curve representing the relationship betweenthe offset values and the amplitude values is determined. An offsetvalue corresponding to the peak of the quadratic curve is determined asan optimum offset value P_(opt1). This procedure is the same as anoffset adjustment processing to be executed when a conventional diskrecording-playback device is initiated into operation.

FIGS. 3 to 5 show a specific procedure of the offset adjustmentprocessing to be executed in step S2 described. A procedure of step S21in FIG. 3 to step S43 in FIG. 5 is the same as the conventionalprocedure shown in FIGS. 13 to 15. In the case where the second pointand the third point are included in four measured points other than thefirst point from among the five points measured, with reference to dataon the first to third points (P_(max), T_(max)), (P_(A), T_(A)) and(P_(B), T_(B)) which are included in the five points measured, therelationship between the offset values and the amplitude values isapproximated to a quadratic curve, calculating an offset valuecorresponding to the peak of the quadratic curve as an optimum offsetvalue P_(opt) in step S43 in FIG. 5.

On the other hand, when the second point is not included in the fourmeasured points other than the first point, the second point isretrieved in steps S30 to S35 in FIG. 4. Data on the second point(P_(A), T_(A)) retrieved is used when the relationship between theoffset values and the amplitude values is approximated to a quadraticcurve in step S43 in FIG. 5.

Furthermore, when the third point is not included in the four measuredpoints other than the first point, the third point is retrieved in stepsS37 to S42 in FIG. 5. Data on the third point (P_(B), T_(B)) retrievedis used when the relationship between the offset values and theamplitude values is approximated to a quadratic curve in step S43.

In step S43 the optimum offset value is determined as described,thereafter followed by step S44 wherein the offset value P_(A) at thesecond point and the offset value P_(B) at the third point are stored ina built-in memory, to terminate the procedure.

Accordingly, the optimum offset value P_(opt) for the focus error isdetermined based on the TE signal, and the focus offset adjustment ismade with reference to the optimum offset value P_(opt). Further, in theoffset adjustment processing to be executed in step S6 in FIG. 2, whichis the same as the processing shown in FIGS. 3 to 5, an optimum offsetvalue for the focus error is determined based on the RF signal, and afocus offset adjustment is made based on the optimum offset value.

With the disk recording-playback device described, the focus offsetadjustment is made based on the TE signal, as described, while the focusoffset adjustment is made based on the RF signal, and signalreproduction and signal recording are thereafter started.

FIG. 6 shows a procedure to be executed by the control circuit 7 in ausual operation for signal reproduction and signal recording after thesystem's initiation into operation. When the usual operation is started,first in step S51 a past disk temperature T_(old) is set at atemperature T₀ stored in the built-in memory in the initiation intooperation of the device as described. In step S52 after the elapse of apredetermined period of time, a current disk temperature T_(now) ismeasured.

Subsequently in step S53 an inquiry is made as to whether the currentdisk temperature T_(now) is not less than a temperature(T_(old)+T_(thr)) obtained by adding the past disk temperature T_(old)to a predetermined temperature T_(thr). When the answer is negative, thesequence returns to step S52 to repeat the same procedure. Here, thepredetermined temperature T_(thr) is set at 5° C., for example.

When variations of the disk temperature in excess of or equal to thepredetermined temperature T_(thr) make the answer for step S53affirmative, the sequence proceeds to step S54 wherein an inquiry ismade as to whether the device is set capable of adjusting variousparameters in accordance with temperature variations of the disk. Whenthe answer for step S54 is negative, the sequence returns to step S52.On the other hand, when the answer is affirmative, step S55 follows toadjust the reproduction power, and thereafter in step S56 the recordingpower is adjusted.

Then in step S57 the focus offset value is adjusted based on the RFsignal, and thereafter in step S58 the focus offset value is adjustedbased on the TE signal. Lastly in step S59 current values of parametersadjusted as described are stored in the built-in memory, and thereafterin step S60 the past disk temperature T_(old) is set at the current disktemperature T_(now). Then the sequence returns to step S52. According tothe procedure described, every time variations in temperature of thedisk in excess of or equal to a predetermined temperature occur, thefocus offset adjustment processing is repeated.

In the previous offset adjustment processing, for example, as seen inFIG. 10, the second and third offset values P₁, P₄ each has an amplitudevalue smaller than the amplitude value T₀ at the first offset value P₀by a predetermined value or more. Further, the optimum offset valueP_(opt1) has an amplitude value greater than the amplitude value T₀ atthe first offset value P₀. Thus the second and third offset values P₁,P₄ each has an amplitude value smaller than an amplitude value T_(opt1)at the optimum offset value P_(opt1) by a predetermined value or more.

Furthermore, when the disk recording-playback device is in the usualreproduction operation, there is little change in the quadratic curverepresenting the relationship between the offset values and theamplitude values. Accordingly, also in the current offset adjustmentprocessing, amplitude values T₁, T₄ at the second and third offsetvalues P₁, P₄ obtained in the previous offset adjustment processing havea very high possibility of being smaller than the amplitude valueT_(opt1) at the previous optimum offset value P_(opt1) by apredetermined value or more, as seen in FIG. 11.

In the focus offset adjustment processing in step S57 and step S58 shownin FIG. 6, focus offset values are respectively set at the optimumoffset value P_(opt1) determined in the previous offset adjustmentprocessing, i.e., the set value concerned, and the previous secondoffset value P₁ and the previous third offset value P₄, as seen in FIG.11, and amplitude values at the respective offset values for the TEsignal or the RF signal are measured. When the second offset value P₁and the third offset value P₄ each has an amplitude value not greaterthan a value (T_(opt1)−5) obtained by subtracting a predetermined valuefrom the amplitude value T_(opt1) at the optimum offset value P_(opt1),a quadratic curve representing the relationship between the offsetvalues and the amplitude values is determined with reference to theoffset values P_(opt1), P₁, P₄ and the amplitude values T_(opt1), T₁, T₄at the respective three measured point. An offset value corresponding tothe peak of the quadratic curve is determined as an optimum offset valueP_(opt2).

FIGS. 7 to 9 show a specific procedure of the focus offset adjustmentprocessing to be executed in step S57 described. First in step S61 inFIG. 7, set to “FALSE” are a P_(A) _(—) flag and a P_(B) _(—) flagindicating whether the second and third offset values P_(A), P_(B) areeach obtained. In step S62, a focus offset value is set at a set valueP₀′ concerned, i.e., the previous optimum offset value, and an amplitudevalue T₀′ for an RF signal is measured.

Subsequently in step S63, a first offset value P_(max)′ is set at theset value P₀′, and a first amplitude value T_(max)′ is set at themeasured amplitude value T₀′. In step S64, offset values arerespectively set at the two values P_(A), P_(B) stored in the built-inmemory, i.e., the second offset and the third offset value used when thequadratic curve is determined in the previous offset adjustmentprocessing, and amplitude values T_(A), T_(B) at the respective offsetvalues are measured.

Next in step S65, an inquiry is made as to whether the measuredamplitude value T_(A) is smaller than the first amplitude value T_(max)′by five steps or more. If the inquiry is answered in the affirmative,step S66 follows to set to “TRUE” the P_(A) _(—) flag indicating whetherthe second offset value is obtained, and thereafter followed by stepS67.

In step S67, an inquiry is made as to whether the measured amplitudevalue T_(B) is smaller than the first amplitude value T_(max)′ by fivesteps or more. If the inquiry is answered in the affirmative, step S68follows to set to “TRUE” the P_(B) _(—) flag indicating whether thethird offset value is obtained, and thereafter followed by step S69 inFIG. 8.

When the amplitude values T_(A), T_(B) at the previous second offsetvalue P_(A) and the third offset value P_(B) are both smaller than thefirst amplitude value T_(max)′ by five steps or more, inquiries in stepS69 in FIG. 8 and in step S76 in FIG. 9 are answered in the affirmative.Then step S83 follows wherein the relationship between the offset valuesand the amplitude values is approximated to a quadratic curve withreference to the data on the three measured points (P_(max)′, T_(max)′),(P_(A), T_(A)) and (P_(B), T_(B)), and an offset value corresponding tothe peak of the quadratic curve is calculated to be an optimum offsetvalue P_(opt). Lastly in step S84, the second offset value P_(A) and thethird offset value P_(B) are stored in the built-in memory, to terminatethe procedure. Accordingly, a new optimum offset value P_(opt) isobtained with reference to the optimum offset value and the second andthird offset values which are obtained in the previous offset adjustmentprocessing, and the amplitude values at the respective offset values.

On the other hand, when the amplitude value T_(A) at the previous secondoffset value P_(A) is not smaller than the first amplitude valueT_(max)′ by five steps or more, an inquiry in step S69 in FIG. 8 isanswered in the negative. In steps S70 to S75, an offset value isdecreased starting from a value smaller than the offset value P_(A) byfour steps, to thereby vary the offset value until when an amplitudevalue T becomes a value smaller than the first amplitude value T_(max)′by five steps or more. Then a second offset value P_(A) and a secondamplitude value T_(A) are respectively set at the offset value and theamplitude value concerned. The second point is thus retrieved.Thereafter in step S83 in FIG. 9, when the relationship between theoffset values and the amplitude values is approximated to a quadraticcurve, the retrieved data (P_(A), T_(A)) on the second point is referredto. However, when an offset value becomes a value smaller than theprevious optimum offset value by 20 steps or more to make the answer instep S71 affirmative, and when an amplitude value T is not greater thana lower limit value T_(L) to make the answer in step S73 affirmative,focus servo deviates, to thereby terminate the procedure.

Furthermore, when the amplitude value T_(B) at the previous third offsetvalue P_(B) is not smaller than the first amplitude value T_(max)′ byfive steps or more, an inquiry in step S76 in FIG. 9 is answered in thenegative. In steps S77 to S82, an offset value is increased startingfrom a value greater than the offset value P_(B) by four steps, tothereby vary the offset value until when the amplitude value T becomes avalue smaller than the first amplitude value T_(max)′ by five steps ormore. Then a third offset value P_(B) and a third amplitude value T_(B)are respectively set at the offset value and the amplitude valueconcerned. The third point is thus retrieved. Thereafter in step S83,when the relationship between the offset values and the amplitude valuesis approximated to a quadratic curve, the retrieved data (P_(B), T_(B))on the third point is referred to. However, when an offset value becomesa value greater than the previous optimum offset value by 20 steps ormore to make the answer in step S78 affirmative, and when an amplitudevalue is not greater than a lower limit value T_(L) to make the answerin step S80 affirmative, focus servo deviates, to thereby terminate theprocedure.

Accordingly, the optimum offset value P_(opt) for the focus error isobtained based on the RF signals, to thereby make a focus offsetadjustment based on the optimum offset value. Furthermore, in the offsetadjustment processing to be executed in step S58 in FIG. 6, the optimumoffset value for the focus error is obtained based on the TF signalsaccording to the same procedure as that in FIGS. 7 to 9, to thereby makea focus offset adjustment based on the offset value. Consequently, focusservo is effected with high accuracy at all times despite variations intemperature of the magneto-optical disk.

In the focus offset adjustment processing to be executed in the usualoperation of the disk recording-playback device embodying the presentinvention, the amplitude values each at the previous offset valueP_(opt1), the previous second offset value P₁, and the previous thirdoffset value P₄ is measured, as seen in FIG. 11. When the amplitudevalues at the second and third offset values P₁, P₄ are both smallerthan the amplitude value at the optimum offset value P_(opt1) by fivesteps or more, the quadratic curve representing the relationship betweenthe offset values and the amplitude values is determined with referenceto the offset values and the amplitude values at the three measuredpoints. This makes a period of time required for the determination ofthe quadratic curve shorter than conventionally, because, with theconventional disk recording-playback device, the amplitude values needbe measured at at least five points. Consequently, a period of timetaken for deriving the optimum offset value is reduced.

Furthermore, when the amplitude value at the previous second offsetvalue fails to be a value smaller than the amplitude value at theprevious optimum offset value by five steps or more, a new offset valueis retrieved wherein an amplitude value is a value smaller than theamplitude value at the previous optimum offset value by five steps ormore, as shown in FIG. 8. Further, when the amplitude value at theprevious third offset value fails to be a value smaller than theamplitude value at the previous optimum offset value by five steps ormore, a new offset value is retrieved wherein an amplitude value is avalue smaller than the amplitude value at the previous optimum offsetvalue by five steps or more, as shown in FIG. 9. Thereafter, a quadraticcurve is determined with reference to the offset value thus retrieved.Accordingly, the quadratic curve is determined with high accuracyconstantly, to thereby obtain the optimum offset value with highaccuracy at all times.

The present invention is not limited to the foregoing embodiment inconstruction but can be modified variously within the technical scopedefined in the appended claims.

For example, in the usual operation, tracking offset adjustmentprocessing can be performed. In this case the optimum offset value canbe obtained in accordance with the procedure shown in FIG. 11.

1. A disk playback device comprising a calculation processing circuitfor determining an optimum value of offset for an error signal based onan amplitude value of the error signal in accordance with focusdeviation or tracking deviation of an optical head or an amplitude valueof an output signal of the optical head, and making an offset adjustmentbased on the optimum offset value, the calculation processing circuitapproximating to a quadratic curve the relationship between offsetvalues and the amplitude values in signal reproduction, and repeatingcalculation of the optimum offset values based on the quadratic curve,and comprising: calculation processing means for approximating to aquadratic curve the relationship between the offset values and theamplitude values with reference to three different offset values andthree amplitude values at the respective offset values, and calculatingan offset value corresponding to the peak of the quadratic curve as theoptimum offset value, and value setting means for setting the threedifferent offset values: a first offset value; a second offset valuesmaller than the first offset value and having an amplitude valuesmaller than an amplitude value at the first offset value by apredetermined value or more; a third offset value greater than the firstoffset value and having an amplitude value smaller than an amplitudevalue at the first offset value by a predetermined value or more, andsetting the three amplitude values respectively at three amplitudevalues at the first to third offset values, the value setting meanssetting the first offset value at an optimum offset value obtained in aprevious optimum offset value calculation processing, and setting thesecond and third offset values respectively at second and third offsetvalues set in a previous optimum offset value calculation processing,wherein a maximum of three amplitude values of a maximum of threedifferent offset values need to be measured to determine the optimumoffset value and the determination of said second and said third offsetvalues does not require the determination of amplitude values of atleast five different offset values.
 2. A disk playback device accordingto claim 1, wherein the calculation processing circuit comprises: firstchecking means for checking whether an amplitude value at the previoussecond offset value is smaller than an amplitude value at the previousoptimum offset value by a predetermined value or more, second checkingmeans for checking whether an amplitude value at the previous thirdoffset value is smaller than an amplitude value at the previous optimumoffset value by a predetermined value or more, the value setting meanscomprising: second offset value setting means for retrieving an offsetvalue having an amplitude value smaller than the amplitude value at theprevious optimum offset value by a predetermined value or more when theamplitude value at the previous second offset value is not found to besmaller than the amplitude value at the previous optimum offset value bya predetermined value or more, and setting a second offset value at theretrieved offset value, and third offset value setting means forretrieving an offset value having an amplitude value smaller than theamplitude value at the previous optimum offset value by a predeterminedvalue or more when the amplitude value at the previous third offsetvalue is not found to be smaller than the amplitude value at theprevious optimum offset value by a predetermined value or more, andsetting a third offset value at the retrieved offset value.
 3. A diskplayback device according to claim 1 or claim 2 wherein the diskplayback device comprises temperature detection means for detecting atemperature of the disk, and the calculation processing circuitcalculates the optimum offset value every time the disk is varied intemperature by a predetermined temperature value.